1. Field of the Invention
The invention relates to methods and apparatus for controlling the resonant frequency of optical interferometer cavities and more particularly to laser frequency control.
2. Description of the Related Art
Lasers and other similar interferometer resonant devices are subject to changes in resonant cavity frequency caused by acceleration forces that cause the physical dimensions of the resonant cavity to vary. In the case of lasers, vibrational forces can cause changes in the optical path length between the cavity reflectors, thus causing changes in the laser output frequency as compared to what would be obtained if the structure were undisturbed or perfectly rigid. Since the performance of many laser devices depends upon the frequency stability of the laser source, freedom from vibrationally-induced frequency changes is an important goal.
In the past, a number of frequency stabilization solutions have been put forward. The main approach has involved an attempt to make the interferometer structure as rigid as possible in order to minimize the effects that vibration has on the dimensions that define the resonant frequency of the interferometer cavity. Another common approach includes passive systems that attempt to isolate the laser structure from vibrations through various shock-mount schemes. Active stabilization has also been used, which involves detection of frequency shifts and the application of correcting forces to the cavity. This involves active electronics, electromechanical type transducers, and other complex devices and circuits. In such active systems, there is the additional problem of accurate detection of the frequency error, which can often be subject to the same vibrationally-induced errors that are causing the need for frequency correction in the main laser system. Additional approaches include devices such as the Spectra-Physics Stabilite, which is a resonator structure mounting system that employs pivots in an attempt to minimize the coupling of torques and other distorting forces to the interferometer cavity. Other approaches utilize various combinations of increased stiffness, shock-mounting, and active stabilization in an attempt to solve the problem. None of the aforementioned approaches, or any combination thereof, provide a solution that is concurrently simple, rugged, and inexpensive.